Write Buffers Filling and high SSD congestion when using deduplication with all NVMe disk groups on vSAN

Products

• VMware vSAN

Issue/Introduction

When using all NVMe devices on VMware VSAN with deduplication, during large bursts of I/O, write buffers can fill and introduce congestion causing latency through the environment. 

Environment

VMware vSAN OSA

Cause

With deduplication, vSAN is only able to de-stage data as fast as the software allows it, this is because the deduplication process takes place during de-staging. Paired with using high performance devices, this can result in a situation where I/O is hitting the write buffers faster than data can be de-staged, causing a bottleneck that results in SSD congestion and cluster wide latency. 

Resolution

Consider turning off deduplication and using compression only for space savings.